Note that figure 2 shows cross-coupled inputs...You can realize an improvement in the signal-to-noise ratio of an amplification system by stacking the system's amplifiers - connecting their inputs in parallel and their outputs in series. You can also modify figure 1's circuit to produce an active balanced transformer (figure 2). This circuit provides the same 3dB noise improvement as in figure 1, the signals add but the noise outputs don't correlate.
"Stacked Amplifiers Lower Noise," Scott Wurcer, Charles Kitchin, EDN, October 13 1982, Figure 2.
"Stacked Amplifiers Lower Noise," Scott Wurcer, Charles Kitchin, EDN, October 13, 1982.
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